CN105484738B - Method for Modeling Conductivity of Fractures in Shale Gas Reservoirs - Google Patents

Abstract

The method for simulating the conductivity of fractures in shale gas reservoirs of the present invention comprises the following steps: making a shale slab and splitting the shale slab into two slab parts. The two slab sections were then tested in a device used to test the conductivity of the fracture. Since the two slate parts are split from shale slabs, the fractures formed by the two slate parts can simulate the conductivity of shear fractures of shale, so that the device can not only simulate the flow rate of volume fracturing fractures Conductivity, can also simulate the conductivity of shear fractures.

Description

Method for Modeling Conductivity of Fractures in Shale Gas Reservoirs

technical field

The invention relates to a method for detecting the characteristics of shale gas reservoirs, in particular to a method for simulating the conductivity of fractures in shale gas reservoirs.

Background technique

Shale gas is a very important unconventional natural gas resource extracted from shale formations. Its formation and enrichment have its own unique characteristics, and it is often distributed in thicker and widely distributed shale gas reservoirs in the basin. However, these shale gas reservoirs have the physical characteristics of low porosity and low permeability. If fracturing is not implemented to form a large-scale fracture network zone and provide sufficient flow channels for shale gas, ideal production will not be obtained. and recovery rate.

At present, the slick water fracturing fluid system is mainly used to fracture shale gas reservoirs. However, the degree of shear dislocation of actual hydraulic fractures, as well as the size and distribution of protrusions are difficult to determine, thus bringing uncertain results to slickwater fracturing in shale gas reservoirs. Therefore, in the prior art, devices for testing the conductivity of fractures are often used to roughly predict the conductivity of shale flow-conducting fractures.

Among them, the formation process of shale fractures used in the device is generally as follows: the main component of the shale to be tested is made into a semicircular model with a groove in the middle, and then the two semicircular models are formed by positive fracturing. A shale fracture with a network of fractures in the middle. However, the shale fractures formed using the above methods can only simulate the conductivity of volumetric fractures under shale gas reservoir conditions.

Therefore, how to solve the existing problem of only simulating the conductivity of volumetric compacted fractures under the condition of shale gas reservoirs is a technical problem to be solved by those skilled in the art.

Contents of the invention

In view of the above problems, the present invention proposes a method for simulating the conductivity of fractures in shale gas reservoirs, which realizes the experimental test of the conductivity of shear-compressed fractures under the conditions of shale gas reservoirs.

The method for simulating the conductivity of fractures in shale gas reservoirs of the present invention comprises the following steps: first making a shale slab and splitting it into two slab parts. The two slab sections were then tested in a device used to test the conductivity of the fracture.

In one embodiment, the two slate sections are compacted before being placed in the device such that a crack is formed between them.

In one embodiment, splitting is performed along the direction of the sedimentary bedding of the shale slab.

In one embodiment, the two rock slab parts are compressed in a state where the two rock slab parts are at least partly staggered or placed facing each other.

In one embodiment, proppant is laid between two of said slate sections.

In one embodiment, the main body of the shale slab is rectangular, wherein both end surfaces thereof are arc-shaped surfaces smoothly connected with two side surfaces of the shale slab.

In one embodiment, prior to placing the slate section into the device, silicone is applied to all surfaces of the slate section that are not intended to form cracks and left to set.

In one embodiment, the proppant is wetted prior to laying it on the slate section.

In one embodiment, after the two slate sections are placed in the device, the closing pressure applied to the two slate sections varies from low to high or remains constant.

Compared with the prior art, the method for simulating the conductivity of fractures in shale gas reservoirs of the present invention includes making a shale slab and splitting the shale slab into two slab parts. The two shale slabs were then tested in a device used to test the conductivity of the fracture. Since the two slate parts are split from shale slabs, the fractures formed by the two slate parts can simulate the conductivity of shear fractures of shale, so that the device can not only simulate the flow rate of volume fracturing fractures Conductivity, can also simulate the conductivity of shear fractures.

Description of drawings

Hereinafter, the present invention will be described in more detail based on the embodiments with reference to the accompanying drawings. In the picture:

Fig. 1 is a flow chart of the method for simulating the conductivity of fractures in shale gas reservoirs of the present invention;

Fig. 2 is a schematic structural view of the shale slab in the present invention.

In the figures, the same parts are given the same reference numerals. The drawings are not drawn to true scale.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

As shown in FIG. 1 , the method for simulating the conductivity of fractures in shale gas reservoirs provided by the present invention includes the steps of making a shale slab 1 and splitting the shale slab 1 into two slab parts. When making the shale slab 1 , the rock samples used to make the shale slab 1 are preferably selected as natural shale cores or shale outcrops to improve the accuracy of the test. When selecting shale outcrops, the same layer should be selected to further improve the accuracy of the test. When selecting shale cores, shale cores with well-developed bedding should be selected to facilitate splitting of the cores.

Furthermore, shale is a rock with a high degree of bedding and natural fractures. Due to its brittle lithology, it is easy to shear and slide along the bedding plane to form shear cracks during hydraulic fracturing. Therefore, in the process of making shale slab 1, the bedding morphology of the target formation must be fully considered feature.

In a specific embodiment, when selecting shale materials, formation cores of target reservoirs or ground shale outcrops should be obtained through drilling. The sampling location of the formation shale outcrop should be consistent with the stratigraphic horizon of the target layer, and the closer to the actual research location, the better. When sampling, first clear the weathered rock layer near the core, and then use mechanical means to excavate large pieces of fresh core along the thickness of the shale.

As shown in Figure 2, the rock sample is processed into a shale slab 1 approximately 17.7 cm long, 4 cm thick, and 3.8 cm wide, so that the shale slab 1 can be placed in a device for testing fracture conductivity experimenting. Further, when processing the shale slab 1, the end face of the shale slab 1 is processed into an arc-shaped surface 12 smoothly connected with the two sides 11 of the shale slab 1, so that the shale slab 1 can be split. Crack, reduce damage to it. And during processing, it should be ensured that the surface of the shale slab 1 is smooth and even.

In addition, when processing the shale slab 1 , the direction of the sedimentary bedding 2 of the shale slab 1 should be parallel to the length direction of the shale slab 1 . In this way, it is convenient to split the shale slab 1 into two slab parts approximately 17.7 cm long, 2 cm thick, and 3.8 cm wide along the direction of the sedimentary bedding 2, thereby preventing the shale slab 1 from splitting. Large fragmentation occurs in the process. Further, after the shale slab 1 is processed, the sedimentary bedding 2 should be basically located near the middle of the shale slab 1, so that the shale slab 1 can be split into two slabs of substantially the same size.

Before splitting the shale rock slab 1, silica gel should be coated on the outside of the shale rock slab 1, and placed until solidified, and then the shale rock slab 1 is split. In this way, the shale rock slab 1 can be prevented from being greatly damaged during the splitting process.

The specific splitting method of the shale slab 1 may be a mechanical splitting method. For example using a splitter to split the shale slab 1 into two slab parts. Fractures formed by splitting can simulate the conductivity of shear fracturing fractures, thus increasing the diversity of experiments. In addition, the fractures formed by splitting also have flow conductivity without proppant, which further increases the diversity of experiments.

After the shale slab 1 is split into two slab parts, the two slab parts are pressed together to increase the accuracy of the experiment. In the first embodiment, the two rock slab parts are staggered by a part first, and then compacted. In this way, the conductivity of dislocated fractures without proppant support can be simulated, so as to more closely match the real situation of the formation. Specifically, the two rock slab parts can be staggered by a certain distance along the length direction, or can be staggered by a certain distance along the width direction. The staggered distance can be determined by the specific test purpose.

In the second embodiment, firstly, the two slate parts are staggered by a part, and the proppant is laid on the two slate parts, and then the two slate parts are compressed. In this way, the proppant-supported conductivity of dislocated fractures can be simulated. The proppant can be selected such as gravel. The thickness of the proppant can be specifically determined according to the actual test purpose, so as to be able to test the influence of the thickness of the sand laying on the conductivity of the fracture. In addition, when laying proppant on the two slate sections, it should be laid evenly to further improve the accuracy of the test. Further, the proppant can be wetted first, and then laid on the slate part. In this way, the rolling of the proppant on the slate section can be reduced, thereby allowing the proppant to be laid evenly on the slate section.

In addition, when testing the conductivity of dislocation fractures, if the volume of the compacted rock slab is too large, the protruding rock slab can be ground. This also facilitates placement in the device when the desired degree of misalignment can be achieved.

In the third embodiment, when the two slate parts are pressed, the two slate parts are placed facing each other. In this way, the conductivity of integrated fractures without proppant support can be simulated. Of course, when two slate parts are positively pressed, the two slate parts may not be absolutely facing each other.

In the fourth embodiment, when the two rock slab parts are compressed, the two rock slab parts are placed facing each other, and a proppant is provided between them. In this way, the conductivity of integrated fractures supported by proppant can be simulated. The thickness of the proppant can also be specifically set according to the needs of the test.

Furthermore, before the two rock slab parts are compacted, the convexity of the surface of the two rock slab parts can be measured first, so as to be able to obtain the roughness of the fracture surface. In this way, the effect of the roughness of the fracture surface on the conductivity can be further studied.

After the two slab sections were compacted, they were tested in a device designed to test the conductivity of the fracture. The device includes a diversion chamber with an annular sleeve inside, and a pressurizing device, a fluid supply device and a fluid measurement device respectively communicated with the diversion chamber. Wherein the annular sleeve is provided with a cavity. When placing, put the rock plate part into the annular sleeve first, and put the annular sleeve into the diversion chamber, and then carry out the test. The way of placing the slab part in the annular sleeve can be determined according to the test requirements.

Then, the closing pressure is applied to the annular sleeve by the pressurizing device, and the experimental test of the conductivity of the crack is carried out. Among them, in the same group of tests, a series of closing pressures can be set from low to high. After the test, the conductivity of the fracture under different closure pressures can be obtained. Of course, a long-term experimental test of the conductivity of the fracture can also be carried out. For example, set a stable closure pressure throughout the test, and then test the variation of the conductivity of the fracture with time.

In addition, before putting the slate part into the annular sleeve, silica gel should be coated on all surfaces of the slab part not used for forming cracks, and put into the annular sleeve after solidification. In this way, the slab part can be prevented from cracking during the test, and the slab part can be more tightly contacted with the wall surface of the annular sleeve, thereby reducing the flow of fluid from the contact surface between the slate part and the annular sleeve during the experiment. throughput.

While the invention has been described with reference to a preferred embodiment, various modifications may be made and equivalents may be substituted for parts thereof without departing from the scope of the invention. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any manner. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims (4)

1. A method for simulating the conductivity of a shale gas reservoir fracture, comprising the steps of: To make shale slabs, split them into two slab parts by mechanical splitting, Test the two slab sections by placing them in a device for testing the conductivity of the fracture; The main body of the shale slab is rectangular, and its two end faces are arc-shaped surfaces smoothly connected to the two sides of the shale slab, so that the direction of the sedimentary bedding of the shale slab is parallel to The length direction of the shale slab; The device includes a diversion chamber with an annular sleeve inside and a pressurizing device communicated with the diversion chamber; the annular sleeve is used to place the slate part, and the closing pressure is applied to the annular sleeve by the pressurizing device ; Before splitting the shale slab, first coat the outside of the shale slab with silica gel, and place it until solidified before splitting the shale slab; Before placing the slate section in the device, apply silicone gel on all surfaces of the slate section not intended to form cracks and allow it to set; Before the two slab parts are pressed together, measure the protrusion on the surface of the two slab parts to obtain the roughness of the crack surface; compressing two of said slate portions before placing them in the device so that a crack is formed between them; splitting along the direction of the sedimentary bedding of the shale slab; laying proppant between two said slate sections; Wet the proppant before laying it on the slate section. 2. The method according to claim 1, wherein the shale slab is made from natural shale cores or shale outcrops. 3. The method according to claim 1 or 2, characterized in that the two rock slab parts are compressed in a state where the two rock slab parts are at least partly offset or in a state where they are placed facing each other. 4. The method according to claim 1, characterized in that after placing the two rock slab parts in the device, the closing pressure applied to the two rock slab parts changes from low to high or remains constant.